Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to welding, and more particularly to a method and apparatus to measure the velocity of a purge gas through the inner diameter of conduit pipe and tubing prior to precision welding.
2. Background of the Invention
Precision welding is required during the fabrication of modern manufacturing plants, food processing equipment, clean rooms, semiconductor and electrical fabrication facilities, etc. Long runs of conduit pipe are often used, which require precision welding of fittings to conduit pipe and tubing, for carrying a variety of process gasses and liquids throughout the facility.
Stainless steel conduit piping and tubing, ranging from 0.0625 inch diameter to about eight inches in diameter is often used in the installation of equipment used during the manufacturing, processing and assembly processes of modern manufacturing and processing facilities. The length of the conduit pipeline, the quantity and quality of welds required, and the purity of the gasses transmitted through the pipeline, often require a consistent, high quality welding technique.
Precision orbital welding is one technique that uses the electrode to orbit around the conduit pipe joint during the welding process, while an inert purge gas flows through the pipeline. Each welded pipe section increases the length and volume of the pipeline, which in turn may vary the purge gas flow characteristics. Back pressure control apparatus is noted in the prior art, but controlling back pressure solves only part of the problem. The velocity of the purge gas passing through the conduit pipe being welded, also significantly affects the quality of the weld.
The pressure of the purge gas is dependent upon the length of the conduit pipe, the size of the pipe, the volume of flow, the number of bends, the number of branches extending from the conduit pipe, and the type of purge gas used.
The problem of controlling the velocity of the purge gas has not been satisfactorily addressed or resolved by the prior art. Thus, this invention both addresses and solves the velocity control problem, improving the quality of weld by significantly reducing problems associated with controlling and removing impurities generated during the welding process, and also the back streaming of contamination from the branch lines into the conduit to be welded, as well as evacuation of the tubing.
The prior art includes U.S. Pat. Nos. 5,864,111 and 6,039,240 by the present inventor, Byron G. Barefoot, issuing Mar. 21, 2000, which discloses a welding backpressure control apparatus. This apparatus effectively controls the internal pressure of purge gas during the welding process, but does not address the problem of establishing the correct velocity or flow of the purge gas for the welding process.
U.S. Pat. No. 5,824,983 issuing Oct. 20, 1998 to Richard Huddleston, Jr., discloses a weld assembly purge restrictor. The purge restrictor is used to control pressure, not velocity of the purge gas. The restrictor does not seal airtight.
U.S. Pat. No. 5,597,109 issuing Jan. 28, 1997 to Tadahiro Ohmi et al., discloses a welding method for forming chromium oxide passivated film at the welded portion. This welding apparatus does not establish the velocity of purge gases prior to the welding process.
U.S. Pat. No. 5,440,096 issuing on Aug. 8, 1995 to Nobukazu Ikeda et al., discloses a welding process with delayed application of full current until after the start of the arc. This patent uses an orifice as a restrictor to create backpressure, and a flow meter to set flow. The orifice does not measure or control the velocity of the purge gas, and does not include a fixed orifice at the outlet end to control the velocity or flow of the purge gas through the system to be welded.
U.S. Pat. No. 5,304,776 issuing on Apr. 19, 1994 to Steven Buerkel, discloses a system for welding pipes, wherein pressure is varied as the welder orbits the pipe being welded, to minimize the undercutting and concavity of the roots of the weld, caused by gravitational effects during the weld process. In this invention, the pressure and flow is varied, whereas in the present application the velocity/flow remains constant.
U.S. Pat. No. 4,845,331 issuing Jul. 4, 1989 to Denis Yeo et al., discloses a pressurized weld chamber. In this patent, constant pressure is provided in a weld chamber, while a shielding gas sweeps away metal vapors. This patent includes a flow meter and needle valve at the outlet, but does not include a fixed orifice to control the velocity of the purge gas.
U.S. Pat. No. 4,723,064 issuing Feb. 2, 1988, to Bill Bothe II, discloses a purge gas system for welding pipes, using a purging plug. There is no teaching in this patent to control the velocity of the purge gas during the welding process by including a fixed orifice to control the velocity/flow of the purge gas. Back pressure is created by hermetically sealing off the end of the pipe to maintain purge gasses within the pipe during welding.
U.S. Pat. No. 3,614,378 issuing Oct. 19, 1971 to Stuart Goodell et al., discloses a fluxless high-frequency aluminum tube welding method, with continuous pressure purging. There is no teaching to control the velocity of the purge gas during the welding process.
Setting of the velocity/flow of purge gas prior to welding, particularly in conduit pipe and tubing, is accomplished by providing a controllably fixed orifice at the distal end of the pipe being welded. The fixed orifice or orifices effectively measures the velocity/flow of the purge gasses prior to welding. The purge gas pressure is preferably from 5 PSI to 100 PSI. The flow is controlled by a metering type shutoff valve.
The purge gas passes through a header connected to the input end of the first conduit pipe section to be welded. The second conduit pipe section to be welded is positioned adjacent to the first conduit pipe to be welded. A pressure clamp or other sealing means is used to seal the circumferential weld area between the first pipe section and the second pipe section. A second pressure gauge monitors the gas pressure at the pressure clamp. Purge gas passing through the first pipe section and over the weld area, then passes through the second pipe section to a manifold with an outlet orifice placed upon the distal end of the second pipe. Purge gas passes through the manifold to the outlet orifice. A back-pressure control means is in fluid communication with the manifold. A first pressure gauge monitor is connected to the manifold, to monitor the pressure of the purge gas as the purge gas passes through the manifold. One or more vent caps, having a controlled orifice size, are airtight and releasably secured to the outlet end of the manifold, to establish the velocity of the purge gas flowing through the conduits and over the area to be welded. Multiple fittings or branch conduit pipe sections may be located on the first or second pipe, and each fitting or conduit has a vent cap with a controlled orifice to control pressure and velocity/flow of the purge gas through each branch connection during welding. This flow is from one percent to ten percent of the flow over the weld.
Thus, one object of this invention is to establish the velocity of the purge gas flowing over the point to be welded prior to welding the joint for improved weld quality and control.
Another object of this invention is to provide vent purge caps on each branch attached to the line to be welded. Each vent purge cap has a controlled orifice size to control the velocity/flow of the purge gas through the branch line pipes during the welding process.
Yet another object of this invention is to provide a selection of vent purge caps, each vent purge cap having a controlled orifice size, the vent purge cap selected according to the diameter of the conduit pipe or fitting to be vented.
Still another object of this invention is to provide a second pressure gauge in fluid communication with the pressure clamp, and a first pressure gauge in fluid communication with the manifold, and velocity/flow is established by pressure readings on the first pressure gauge, and the second pressure gauge is used to set pressure at the weld site.
Other objects, features and advantages of this invention will become obvious to one of average skill in this art upon consideration of the following description when read in conjunction with the following drawings.